Parts questions

Hi -

I'm working on assembling some parts to build my 1st HeaterMeter and had a few questions.

Header - would this work (yes, more expensive than DigiKey, but one shipping charge less)
Mouser 26 pin header

Fan - I have a few of these beasts of fans sitting around. Is there a problem with using a bigger fan?
http://www.digikey.com/product-detail/en/RL90-18%2F12N/381-1059-ND/387665?enterprise=2
img.ebmpapst.com/products/datasheets/DC-centrifugal-fan-RL901812N-ENG.pdf
It appears to push ~3x the volume of air if left at full output. Fwiw, I'm this will be attaching to a Large BGE.

Thanks
Job

That fan is HUGE physically but the output isn't that over the top. You can limit the top speed of the fan with the HM to prevent it from blowing too hard and kicking up ash. I see no reason why it wouldn't work, the biggest issue would be how slow can it go? I just got a 25 CFM fan to try because the stock HM fan wasn't putting out enough air for my high heat Pizza cooks. It seems the bigger fan (I have) isn't capable of putting out as slow of a trickle of air as the small HM fan does, so it is possible the temp may be a little more rocky with the larger fan, but it should work. If you have them available on hand for free there is no harm in trying, it should work, if you find the slowest speed is too high for your smoker you can always order the smaller fan and swap it out. The good news is if it does work for low and slow cooks it will also have the extra capacity to stoke your fire pit up to pizza oven temps if you want....

Cool. I'll try it with this fan, and see how it goes. I was thinking about physically baffling the fan - which has the nice side effect of lowering the power consumption.

I have lots of muffin fans around, so I might end up with a high-heat fan, and a low-and-slow fan too. That's what plugs are for, right?

I'm guessing that a muffin fan can generate enough static pressure for the low end of things?

Thanks
job

Speaking of power consumption.....

I should have mentioned that you might want to beef up the Power Supply wattage a bit if you plan on using a bigger than stock fan. I went with a 24W/2A PS instead of the suggested model because I anticipated using a larger fan down the line. This weekend I just installed my 25CFM fan for the first time, when I tested it with a smaller wattage power supply the HM would brown out and reset when the fan speed went a bit above 50%, but it runs just fine at 100% with the 24W/2A PS. So the PS might be the one item in the HM build that need be changed/upgraded to support a larger fan.

I also have the stock 6.7CFM fan, and as you suggested, I think I will be using the 6.7CFM fan for low and slow cooks and the 25CFM for higher heat cooks. I have the servo damper as well, and have been running the pit in dual mode with the fan and servo damper lately, with the fan set to run only at 100%. In this mode it doesn't matter if I use the bigger fan or smaller fan (for lower temp cooks), because you can limit the max speed of the fan which will set the speed the fan will blow when it turns on. In this mode the fan does not need to run at a trickle pace, it just blows at one speed at a fairly high rate because it is only on when the pit needs the HM to be running at 100%.

Thanks for the heads up on the power consumption. My blower is labeled 12W, so it might be best to get a >12W power supply. I would not have thought of that before hooking it up.

Not to hijack my own thread, but...

One thing this blower, and many, many surplus fans have is a tach wire/pin. It might be interesting to hook that up and see how things are moving. I think I read that there was one spare input left on the AVR... But I've never worked with either the AVR, or fan tachometers before. I think the tach is a hall sensor that pulses with rotation. That is you get a pulse for each rotation.
http://www.themakersworkbench.com/content/tutorial/reading-pc-fan-rpm-arduino

Has anyone tried this?

I'm not completely sure, but I think Bryan tasked that last input on the AVR for the servo, so it can be run at the same time as the fan...

There's still technically 1 more digital and 1 more analog pin left, but the digital would mean having a third version of the AVR firmware and maintaining 2 versions is already enough fun. The fan tach signal doesn't work anyway though, because it relies on getting DC voltage ~7-12V and HeaterMeter pulses the fan on and off 12V/0V. The 12V on pulses might actually be long enough for enough fan tach pulses to get a semi-accurate reading though.

So, I got the last part today (PCB), and soldered it all up. Works pretty well here on the bench so far. I'll hook up the fan and give it a test run tomorrow.

The step by step photos are awesome. The only thing that might help is some help finding where each location is on the board. Maybe arrows on the assembly pictures or just a version of the PCB design. I checked the png of the board, but it has all the layers and is backwards. Harder to use than just scanning the board. That's a pretty minor quible.

A few wiki thoughts while Bryan is planning on correcting the servo stuff tomorrow. (and, yes, I'm happy to edit myself if you want to give me access.)

The RCA connector that you de-solder from the Pi is an almost perfect match for the one on the HM part list. Might be nice to note that you can just use it. I was not 100% sure about the pin locations, so I now have an extra RCA for the next project.

Something about power supply wattage might be good to note near the blower on the part list or asm page. (see discussion above in this thread)

It might be good to note that you only can only get 4 temps no matter the source. I was not sure if by adding the RFM12B I might be able to get a temp from my weather station in addition to the 4 probe temps.

In the asm instructions, the early steps have part ids (R1, C3), but the later ones do not. That would be nice, and make it quicker to find the right part. I had to poke around at the parts for a minute or two to find the power regulator (aka IC1).

The orientation of the RFM12B is not clear without looking up the spec sheet.

Is it worth putting a servo on the Optional Parts list yet?

Some of the parts are also available at Modern Devices (power header, DIP blocks, etc.) Not sure if it's worth adding them to the list in case parts are out of stock at Mouser/Digi.

Thanks for the suggestions, I've included some of them in the wiki.

Yeah the png of the board is backward because most the parts are on the bottom. As you found the png of the board is just a picture of the board, and if you have a board then it is easier to just look at it to find where the parts go.

The RCA is an identical part actually, or at least it used to be when the first Pis were rolling off the line. I updated the parts list to suggest it can be used but it can be a pain to remove so I wouldn't recommend anyone omit the part from their purchase in case they wreck it trying to take it off.

The power supply is always listed as 12V / 1A, which is how they're labeled. Did I miss one somewhere? I think saying 12W power supply adds too much information considering I rarely see anything labeled as a 12V/12W power supply.

I'm not sure where to put the indication that even with RFM12B you'll only have 4 probes. It is a good idea though. Suggestions where to put it?

The RFM12B is oriented to match the silkscreen, oval over oval. That may not be obvious though, you're right.

The servo will go on the optional parts list in the v4.1 board information. I'll have to remember that when the time comes.

WRT the PCB image... The problem I had on a few parts is that the silkscreened part names were smooshed/overtyped such that it was pretty hard to read. The ones I remember most were the 390k resistors. Between the name (R10 for example) and the resistance value, you could not really read either. I guess this is really more of an issue w/ OSHPark? Not a huge deal, just took some time to sort out.

For the power supply: It's not the labeling I was thinking of, but the power/headroom. I'm reusing a blower from a disk tray, which turns out to draw (max) 2A/24W. A note on the part list to make sure your power supply has enough power for whatever fan you use. RalphTrimble saved me from this in the discussion above.

To note the 4 probe limit, perhaps there should be a caveats/warning section of the wiki? 4 probe limit, 24 hour rolling data window, probe max temp of ~500 usable, no gui for automatic setpoint changes (but can be done via alarms and scripts), etc. Otherwise, it probably makes sense to note it in the parts list both by TR1 and by U$1?

For orienting the RFM12B, the one I got had no oval blob. (the one on the bottom right in the Modern Devices website image - http://moderndevice.com/product/rfm12b-radio/) It would be easy to guess that the round black blob is the oval on the PCB. Maybe the oval should be a rectangle to match the silkscreened one on the RFM12B? Or a circle and rectangle?

One tool that might be good to add to the list is some solder wick. I used a bit for removing the rPi RCA, but for more inexperienced solderers it's invaluable.

Thanks again. I still have not fired it up for a real smoke (work & sick), but will soon.

job

Oh, and thinking of power, the PS should have enough umph for the servo too. Not that I can find that info on Futaba's site for the one I got.